Circuit breaker



' y May 7, 1940- H. D. DORFMAN 2,199,622

CIRCUIT BREAKER Filed July 51, 1937 wl'rNEs'sEs: lNvENToR @Mmm @W2/M Patented May 7, 1940 UNITED STATES PATENT OFFICE CIRCUIT BREAKER Pennsylvania Application July 31, 1937, Serial No. 156,769

12 Claims.

The invention relates to circuit breakers in general and more particularly to circuit breaker trip devices which utilize a thermally responsive bimetallic trip element.

'Ihe bimetallic trip elements of circuit breakers used in controlling lighting and moderate power industrial feeder circuits are often subjected to extremely high overload currents before the circuit is interrupted, due tothe interconnection of a large number of circuits. The trip element should therefore be of such dimension as to carry such high overload currents without damage. When'the bimetal trip element is the sole protecting means embodied in the breaker, it must pass low magnitude overload currents which are of short duration without tripping the breaker and yet be operable to trip the breaker when low magnitude overloads persist for more than a predetermined length of time. The bimetal trip element should also operate in the shortest possible period of time to trip the breaker in response to high magnitude overloads. In addition to the above functions, the bimetal trip element must be capable of being mounted in a very small space to reduce the space occupied by the breaker.

An objectspi/the invention is the provision of a circuit breaker embodying an improved bimetallic trip element which satisfies all of the above-mentioned requirements.

Another object of the invention is the provision of an improved current carrying bimetallic trip element for a. circuit breaker, which is capable of carrying extremely high overload currents without damage and yet which occupies a very small amount of` space and is operable to trip the breaker in response to low magnitude overloads of predetermined duration.

Another object of the invention is the provision of an improved bimetallic trip element for a circuit breaker, which is capable of carrying considerably higher overload currentsl than bimetallic trip elements of the same rating heretofore known and yet which is mountable in the same height space and has the same resistanceand is capable of the same amount of deection in response to low magnitude overloads.

Another obiect of the invention is the provision of an improved current carrying bimetallic trip element for a circuit breaker which has a greater o cross section and length than bimetal trip elements of the same rating heretofore known so that it can carry greater overload currents without damage and yet which can deflect the same amount in response to lower overloads, the bimetallic trip element being so formed that-it can (Cl. 20o-116) be mounted in the same small space as the known bimetal trip elements of the same rating which have less length and cross section.

Another object of the invention is the provision of an improved current carrying bimetallic trip element for circuit breakers, which has a greater cross section and length than bimetal trip elements of the same rating heretofore known or used, and yet which is mountable in the same small space and operable to trip the breaker within the same time limit in response to low magnitude overloads and in considerably less time in response to high magnitude overloads.

'I'he novel features that are considered characteristic of the invention are set forth in'par- 15 ticular in the appended c1aims. The invention itself, however, both as to structure and operation, together with additional objects and advantages thereof will be understood from the following detailed description of several preferred em- 20 bodiments thereof whenlread in connection with the accompanying drawing, in which Figure 1 is a vertical sectional view of a circuit breaker embodying the features of the invention. Fig. 2 is an enlarged side elevational view of the bimetallic trip element shown in Fig. l, the

able contact Il for cooperating with thesta-v `tionary contact, operating means indicated generally at I3 for the pivoted switch member, a trip device indicated generally at I5 and a cover I1 also of molded insulating material for enclosing and protecting the breaker operating mechanism.

The breaker is provided with a pair of end terminals I9 and. 2| secured in recesses formed in y the opposite ends of the base 5, by means of screws 23. 'I'he terminals!! and 2l are provided with terminal screws 25 for connecting the circuit' breaker in an electrical circuit.

The stationary contact 'I is secured to the base' 5 by means of a screw 21 and is connected to the end terminal 2| by means 29 and the screws 21 and 23.

'Ihe operating mechanism I3 and pivoted switch member 9 are supported by a U-shaped main frame 3| secured to the base 5 by means of suitable screws 33.

a modified 30 of a conductor strip The switch member 9, which carries the movable contact at one end, comprises a resilient spring strip secured at its other end to a channel shaped support 35 by means of suitable rivets. The channel shaped support 35 is pivotally secured to the frame between the side walls thereof by means of a pivot pin 31.

An arc extinguishing means, indicated generally at 39, of the spaced plate type is associated with the stationary contact 1 and the movable contact The arc extinguishing means serves to quickly extinguish the arc formed incident to the separation of the contacts during circuit interruption. Any suitable type of arc extinguishing means may be used. One preferred form of arc extinguishing means is described in Patent No. 2,044,157, issued to Hiller D. Dorfman and John H. Schuler, June 16, 1936, and assigned to the assignee of this invention.

The operating mechanism for the circuit breaker comprises, in general, an actuating toggle consisting of a pair of toggle links 4| and 43, a pivoted carrier 45 for the upper end of the toggle, an overcenter spring 41 and a bifurcated operating lever 49. 'Ihe toggle links 4| and 43 are pivotally joined together by a knee pivot pin 5|. The lower end of the toggle link 43 is pivotally connected to the channel shaped contact support 35 by means of a pivot pin 53, while the upper toggle link 4| is pivotally connected at its upper end to the pivoted carrier 45 by means of a pivot pin 55. The overcenter spring 41 is connected at its lower end to the knee pivot pin of the actuating toggle and at its upper end to the top of the bifurcated operating lever 49, which is pivoted to the side walls of the main frame at 51. The upper ends of the side Walls of the main frame 3| are oiset and notched, as indicated at 59, for limiting rocking movement of the operating lever 49. An operating handle 6| of molded insulating material is secured to the upper end of the lever 49. The haandle 6| is provided with an operating knob 63 which projects through an opening 65 provided therefor in the cover |1, and also with an arcuate cover portion 61 which serves to cover the opening 65 in any position of the operating lever 49.

The carrier member 45 is pivoted to the main frame 3| by means of a pivot pin 69 and is provided with an extended latch portion 1|. The clockwise movement vof the carrier 45 about its pivot axis 69 is limited by a stop bracket 13 formed integral with one of the side walls of the main frame 3|. The carrier 45 is at all times biased in a clockwise direction about its pivot axis 69 by'a component of force exerted by the overcenter spring 41, but is restrained in the normal position `shown in Fig. 1, in which "it holds the upper' end of the actuating toggle in operative position by means of va latch carried by the trip device which will be hereinafter described. The operatingV lever 49 is provided with ya hook shaped projection 15 yfor engaging and moving the carrier A45 in acounter clockwise direction to its normal latched position to-reset the same following a tripping operation.

The jcircuitthrough the breaker extends from the left-hand' nd terminal |9 through a flexible shunticonduc'tor '11, through the trip device I5, pivoted switch member 9, movable contact stationary' contacty 1, and conductor strip 29 to the vopposite or right-hand end 4terminal 2|.

AThe"circuit breaker is shown in the closed position in Fig. l and it will be noted that the knee ci the actuating toggle is in the overset or made position, holding the contacts 1 and in pressure engagement, the carrier 45 being held in latched position by the trip device to maintain the upper end of the actuating toggle in operative position. To open the contacts manually, the operating handle 6| is moved in the counterclockwise direction'about its pivot axis 51; shortly before the operating handle 6| has reached its limit of travel in the counter-clockwise direction the line of action of the overcenter spring 41 is brought to the left of the center line of the toggle. This results in the producing of a component of force which moves the toggle to the collapsed position. Since the movement of the knee of the toggle from the position shown in Fig. 1 toward the collapsed position results in a progressive increasing of the force causing the movement, the opening operation once started takes place automatically and results in the separation of the contacts with a snap action.

The manual closing operation is substantially the reverse of' the opening operation. The operating handle 6| is moved in a clockwise direction, the resulting tension of the overcenter spring 41 as it crosses the center line of the toggle causes the knee of the toggle to move toward the closed circuit position. The spring 41 thus acts to move the actuating toggle to the overset or made position shown in Fig. 1 to effect clockwise movement of the switch member 9 about its pivot pin 31 to closed circuit position. 'Ihe closing movement of the switch member 9 is likewise carried on with a snap action.

When an overload of suicient magnitude and duration occurs in the circuit controlled by the breaker, the trip device |5 operates to release the pivoted carrier 45. The release of the carrier 45 allows that member to move freely in a clockwise direction about its pivot pin 69 under the influence of the overcenter spring 41. Almost immediately the end of the toggle link 4|, which is pivoted to the carrier 45, is moved a suiicient distance to the right of the center line of the toggle to cause the toggle to collapse as a result of the tension force applied to the knee pivot pin 5| by the overcenter spring 41. The collapse of the toggle causes the switch member 9 to be rotated in a counter-clockwise direction about its pivot axis 31 to its open circuit position to separate the contacts in the same manner as described for the manual operation. The tripping operation is also carried on with a snap action. It will be observed that the switch member 9 is trip free of the operating handle 6|, that is to say, the contacts are opened when the carrier 45 is released during a tripping operation irrespective of the position in which the operating handle 6| may be held.

Following the tripping operation and the resulting change in the position of the knee pivot pin'5|, the operating handle 6| is biased in a counter-clockwise direction and moves to an intermediate indicating position to show that the circuit breaker has been opened in response to an overload condition. Before the breaker can be closed again, it is necessary to reset the carrier 45 to its latched position shown in Fig. 1. To reset the mechanism the operating handle 6| is moved tothe full open position. This movement causes the hook shaped extension 15 to engage and rotate the carrier 45 in the counterv clockwise direction about its pivot pin 69 to reengage the latch portion 1| of the carrier in latching engagement with the latch of the trip device.

The trip device indicated generally at I5 comprises a strip 19 of bimetallic material secured at its lower end to the base 5 of the breaker by means of a screw 8| which engages a threaded insert 83 held in the base 5. 'I'he screw 8| in addition to mounting the trip device and positioning the same with respect to the operating mechanism also serves to electrically connect the lower end of the strip to the pivoted switch member 9. 'I'his connection is effected by means of a flexible shunt conductor 85 connected at one end to the screw 8| and its other end to the pivoted swit-ch member 9. The upper free end of the bimetallic strip 19. is provided with ay latch plate 81 for` engaging the latch portion 1| of the carrier 45 in overlapping relation to normally restrain the carrier. The latch plate 81 is secured to the upper free end of the bimetallic strip 19 by means of a rivet 88 and is insulated from the strip by a pair of mica plates 89. The terminal I9 is electrically connected to the upper free end of the bimetallic strip 19 by means of the flexible conductor 11, as shown in Fig. l. The bimetallic strip or trip element 19 has sharp reversed loops k9| and 93 bent therein adjacent its angularly bent base 95, and a vertically disposed straight portion 91 to the upper free end of which the latch plate 81 is secured. 'I'he high expansion side of the bimetallic trip element 19 is disposed adjacent the operating mechanism I3 so that when the strip is heated a predetermined amount in response to an overload current, it delects away from the operating mechanism to effect release of the carrier 45.

The specific formation or structure of the bimetallic tripelement 19, particularly the sharp reverse loops formed therein, provides a trip element which has a number of advantages over the conventional forms of thermally responsive trip elements that have heretofore been known or used. The cross sectional area of the trip element 19 is of suilicient size so that the trip element can carry extremely high overload currents during circuit interruption without damage to the element. The increased cross section of the bimetallic trip element also provides the necessary degree of stiiness of the element so that it is easily able to overcome the latch load in releasing the carrier 45. This permits a strong overcenter spring to be used in connection with the operating mechanism of the breaker so that a quicker make and break action for the contacts may be secured. The sharp reverse loops 9| and 93 provide the bimetallictrip element with an actual length a number of times greater than its longest dimension, or height in the present instance, so that the bimetal trip element deflects a suilcient amount in response to overloads of predetermined low magnitude and duration to effect 4release of the carrier 45. In other words, even though the cross sectional area and current carrying capacity of the bimetallic trip element is considerably greater than a straight tripl element of less lcross section and current carrying capacity, yet the trip element 19 has substantially the same resistance and= is capable of deflecting the same or even a greater amount in response to low magnitudev overloads because of its increased length. The sharp reverse loops 9| and 93 reduce the height of the bimetallic trip element so that it can be mounted in a relatively small space, thus permitting the breaker to be made very compact.

The sharp reverse loops 9| and 93 in the bimetallic trip element provide a. number of advantages in the operating characteristics of the trip element over the conventional thermally responsive trip elements heretofore known or used. The sharp bends of the loops 9| and 93 are so located as to produce maximum deection of the upper free end of the trip element. When the trip element is heated a predetermined amount, the resulting bending of the element at the bends of the loops 9| and 93 causes deilection of the straight portion 91 so that the free end is deflected a considerable amount over and above that produced by the flexing of the straight portion 91. The sharp reverse loops 9| and 93, in addition to producing the above-mentioned advantage, also reduce the heat radiation losses at the portion of the bimetallic trip element which produces 'the greatest deilection, so that the deilection of the trip element in response to high magnitude overload currents is accelerated a considerable amount. It will be noted that there are three sharp bends indicated at 99, Illl and |03 in the bimetallic trip element. in owing through' the trip element tends to follow the shortest path and thus crowd into the high expansion side of the trip element at two of these bends 99 and |03, whereas it crowds the low expansion side at only one bend This crowding of the current in the two sharp bends heats the high expansion side of the bends more than the low expansion side [which considerably increases the deflection of the upper free end of the trip element. It will also be noted that the current in flowing through the reverse loops 9|93 of the trip element 19 flows in opposite directions' as indicated by the arrows in Fig. 2, so that the straight portions of the loops 9| and 93 tend to magnetically repel each other. 'I'hese repelling forces also increase the deflection of the free or latch carrying end of the trip element.

currents, which is a particularly desirable result.y

The operation of the trip device is briefly as follows: When anI overload current of predetermined low magnitude and duration occurs in the circuit controlled by the breaker, the increased 12R loss in the current carrying bimetallic trip element 19 results in the production of suiiicient heat to cause that element to deflect away from the operating mechanism I3 to effect release of the carrier 45 and opening of the contacts in the manner previously described. Likewise, when an overload of high magnitude occurs in the circuit controlled by the breaker, the bimetallic trip element deflects in the same manner to effect release of the carrier 45 but acts in considerably shorter time. The bimetallic trip element in deflecting moves away and downwardly with respect to the carrier 45. The bimetallic trip element 19 may be made the same width throughout its entire length or may be tapered toward its upper end to increase the resistance thereof, if desired.

A slightly modified form of the bimetallic trip element is shown in Fig. 4. The same reference characters have been used in designating the corresponding parts of this modification of the trip device as in the trip device shown in Figs. 1 and The three factors mentioned above, namely, the reduction of the heat radiation 'I'he current A 2 except that prime marks have been added. In this modification, the bimetallic trip element I8 is provided with sharp reversed loops Sl' and 93 which are disposed horizontally instead of vertically as in the case of the trip element shown in Figs. 1 and 2. This modified form of trip element .possesses the same advantages and functions in substantially the same manner as the trip element described in connection with Figs. 1 and 2, except that the free or latch carrying end thereof deflects away and upwardly with respect to the latch portion H of the carrier when the element is heated a predetermined amount in response to overload conditions.

While the invention has been disclosed in accordance with the provisions of the patent statutes, it is to ybe understood that various changes in the structural details thereof may be made without departing from the spirit of the invention. It is desired, therefore, that the appended claims vbe given the broadest reasonable construction permissible in the light of the prior art.

I claim as my invention:

1. In electrical apparatus, a current carrying bimetallic control element comprising a strip of bimetallic material having sharp reverse loops bent therein adjacent its base, said loops having leg portions which are all disposed substantially parallel and close to each other, the current in flowing through said element crowding the high expansion side at the majority of the sharp curves of said loops to effect an increased deflection or the element.

2. In electrical apparatus, a current carrying bimetallic trip element having sharp reverse loops formed therein `adjacent its lbase substantially perpendicular to the base, said loops having leg portions which are all disposed substantially parallel and close .to each other so as to reduce heat radiation losses at said loops and increase the deflection of said element.

3. In an electrical apparatus, a current carrying bimetallic Itrip element having sharp reverse loops formed therein adjacent its base, said loops having leg portions which are all disposed substantially parallel and close to each other to reduce heat radiation losses at said loop and accelerate ydeflection of said element in response to high magnitude overload currents.

4. In electrical apparatus, a current carrying bimetallic trip element having sharp reverse loops formed therein adjacent the base, said loops having leg portions which are all disposed substantially parallel and close to each other so that the current ilows in opposite directions at said looped portion in flowing through said element and produces repelling magnetic el-ds which increase the deflection of said element.

5. In electrical apparatus, a current carrying bimetallic trip element having sharp reverse loops for-med therein adjacent the base, said loops having leg portions which are all disposed substantially parallel and close to each other so that Ithe current ilows in opposite directions at said looped portion in flowing through said element and produces repelling magnetic elds which accelerate and increase the deflection of said element in response to high magnitude overload currents.

6. In electrical apparatus, a current carrying bimetallic control element having sharp reverse loops formed therein adjacent its base and disposed at an angle to said base, said element having sufficient cross section to carry extremely high magnitude currents, said loops having leg portions which are all disposed substantially parallel and close to each other providing said control element with an actual length considerably greater than the longest dimension of the element so as to provide sumcient resistance and deflection of said element in response to predetermined low magnitude values ol" current.

7. In electrical apparatus, a current carrying bimetallic control element comprising a strip of bimetallic material having a base, sharp reverse loops adjacent said base and disposed at an angle to said base and a vertically disposed straight portion of greater length than said loops, said loops having leg portions which are all disposed substantially parallel and close to each other to deflect said vertical straight portion when said element is heated a predetermined amount.

8. In a circuit breaker, contact means, actuating means for said contact means including a normally restrained spring biased opening member releasable to eect opening of said contacts, a current carrying bimetallic trip element xed at one end and carrying a latch adjacent its free end for normally restraining said opening member against opening movement terminating in the free end, said element having a straight portion, and at least one U shaped loop having leg portions which are disposed substantially parallel and close to each other and parallel to the straight portion and formed in said element adjacent the fixed end of the element, the force applied to the free end of said trip element by said opening member as a result of its bias, being parallel to the straight portion and the loops of the element. v

9. In a circuit breaker, relatively movable contacts, actuating means for opening and closing said contacts, a trip device operable to cause said actuating means to open said contacts comprising a current carrying bimetallic trip element connected in circuit with said contacts having suilicient cross section to carry extremely high values of current without damage and having sharp reverse loops adjacent its base, said loops having leg portions which are disposed substantially parallel and close to each other providing increased deilection ol' said clement in response to overloads of predetermined low magnitude and duration to trip said breaker and causing an accelerated deilection of said trip element to trip said breaker more quickly in response to higher magnitude overloads.

10. In a circuit breaker relatively movable contacts, actuating means for said contacts including a normally restrained spring biased opening member releasable to eiTect opening of said contacts, releasable latch means for normally restraining said member, a current carrying bimetallic trip element operable in response to predetermined overload conditions to release said latch means, said element having suflicient cross section to carry extremely high overload currents without damage and to provide sullicient stiffness to overcome the latch load to release said latch means and opening member, and having sharp reverse loops ben-t therein adjacent its base, said loops having leg portions which are disposed substantially parallel and close to each other. the current in flowing through said loops producing repelling magnetic elds which aid in deecting the free end of said element to trip said breaker.

11. In a circuit breaker, Contact means, actuating means for opening and closing said contact means including a normally restrained spring biased opening member releasable to eie'ct opening of said contacts, a current carrying bimetallic trip element iixed at one end and carrying a latch adjacent its free end for normally restraining said opening member, said element having a vertically disposed straight portion, a vertically disposed U shaped loop .bent therein adjacent its fixed end and its iixed end lient angularly with respect to the straight portion and the loop, said loop having leg portions which are substantially parallel and close to each other.

12. In a 'circuit breaker, contact means, actuating means for opening and closing said contact loop having leg portions which are substantially 10 parallel and lclose to each other, l Hmmm D. DORFMAN. 

